docs: def maxDepth(self, currentDepth=0):
          """Compute the depth of the longest branch of the tree"""
          if not any((self.left, self.right)):
              return currentDepth
          result = 0
          for child in (self.left, self.right):
              if child:
                  result = max(result, child.maxDepth(currentDepth + 1))
          return result